The present invention claims the benefit of Korean Patent Application No. P2000-64526 filed in Korea on Nov. 1, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to an etchant used during copper etching in a semiconductor substrate fabrication process, and more particularly, to an etchant with an additive to control change in the copper etch rate over passage of time and also to a method of fabricating a substrate for an electronic device using the additive-containing etchant.
2. Discussion of the Related Art
A substrate can be used to fabricate various electronic devices such as a thin film transistor (TFT) for a liquid crystal display (LCD) device, a solar battery, an electroluminescent display device, or a touch panel. The substrate for an electronic device includes lines and electrodes of various patterns for driving the device. A Cu deposition film, for example, Cu or Cu/Ti (Titanium) having excellent low resistance characteristics, is mainly used as a material for the above-mentioned lines and electrodes. To form desired lines and electrodes by using a material such as Cu or Cu/Ti, photolithography and etching processes must be performed on the substrate.
A related art etchant and a method for fabricating a substrate for an electronic device using that etchant is explained below with reference to FIGS. 1 and 2.
FIG. 1 is a plane view of a general TFT substrate, and FIG. 2 is a graph showing variations in etch rate against the number of sheets of processed substrates according to the related art. The TFT substrate is an example of a substrate for an electronic device, and the TFT is a constituent part of a TFT-LCD panel. As shown in FIG. 1, the TFT substrate includes gate lines 1 and data lines 2 arranged in a matrix form that divides a unit pixel; a TFT (of elements 4-7) formed on a crossing point between a gate line 1 and a data line 2; and a pixel electrode 9 electrically connected to the TFT.
As shown in FIG. 1, the TFT includes deposition films for a gate electrode 4, a semiconductor layer 5, a source electrode 6 and a drain electrode 7. The TFT serves as a switching device that turns a data signal on and off according to a scanned gate voltage applied to its gate electrode 4.
To form the patterns for gate lines, data lines and various electrodes, photolithography and etching processes must be performed on the TFT substrate. The photolithography relies on a chemical reaction in which a specific photoresist reacts chemically to light and changes its own properties. During photolithography, the desired circuit pattern is formed on the substrate using a mask and selective irradiation of light onto the substrate with the mask. Thereafter, the mask is removed and the substrate is etched to obtain the desired circuit pattern on the substrate.
Etching is a process used after photolithography to selectively eliminate the photoresist and other deposition films along patterns formed on the photoresist to obtain a real thin film circuit pattern. The etching process uses physical and chemical methods and consists of both dry-etching in which a gas is used and wet-etching in which an etchant such as acid liquid is used. It is noted that to etch a Cu deposition film of, for example, Cu or Cu/Ti, a wet-etching is preferably used.
Thus, the gate lines, the gate electrodes, the data lines, and the source and drain electrodes are finally formed with a wet-etching of a Cu deposition film using an etchant. Some examples of related art etchants include a Cu etchant containing KHSO5; a Cu/Ti etchant containing HF, KF, and KHSO5; or a Cu/Ta etchant.
An etching reaction of Cu is derived from hydrolysis of KSHO5, that is, KHSO5+H2= greater than KHSO4+H2O2. The following formulas 1 and 2 express the etching reactions of Cu.
Cu+KHSO5== greater than CuO+KHSO4xe2x80x83xe2x80x83[Formula-1]
Cu+KHSO5== greater than CuSO4+2K2SO4+2H2O+O2xe2x80x83xe2x80x83[Formula-2]
However, as shown in FIG. 2, when a single layer of copper (Cu) is wet-etched, the etch rate of Cu is not constant per number of sheets of processed substrates that include the single layer of Cu. The etch rate, as shown in FIG. 2 increases or decreases depending on the number of sheets of processed substrates. The increase in etch rate is caused by a reaction resulting in CuSO4 that has an increased concentration as the Cu film is etched. The generated CuSO4 increases the etch rate of Cu.
Table-1 given hereinbelow shows a critical dimension loss (CD-loss) of a Cu/Ti (1500 xc3x85/300 xc3x85) deposition film and a xcex94L according to the number of sheets of processed substrates that include the Cu deposition film, where the Cu/Ti deposition film is etched by an etchant in which HF, KF, and oxone are mixed with a rate of 0.1%, 0,2%, and 2% respectively. The oxone, as used herein, is a mixture of 2 KHSO5, KHSO4, and K2SO4. In Table-1, the CD-loss represents a length difference between a desired pattern length and an etched pattern length that is etched more than the desired pattern length. The xcex94L is a numerical value obtained by subtracting the initial CD-loss from the CD-loss of the corresponding number of sheets of processed substrates.
Table-1, like FIG. 2, demonstrates that the etch rate varies as the number of sheets of processed substrates increases. This change in the etch rate over passage of time makes a uniform management of a Cu profile difficult, which causes deterioration in yield.
To obtain a uniform Cu pattern profile with a related art etchant, the etchant should be replaced after processing 450 sheets of substrates, leading to complicated processes and increased production costs due to increased etchant consumption.
Thus, a related art method of fabricating the substrate for an electronic device has the following problems. First, since it is difficult to manage a pattern profile uniformly because of the change in the etch rate over the passage of time when a deposition film of Cu or Cu/Ti is etched by a related art etchant, devices with inferior accuracy are produced. Second, to obtain a profile of a uniform Cu pattern, the prior art etchant must be replaced periodically. Because the period for replacing an etchant becomes short, the production cost increases.
Accordingly, the present invention is directed to an etchant and a method for fabricating a substrate for an electronic device using that etchant. The etchant and the method of the present invention substantially obviate one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an etchant and a method for fabricating a substrate for an electronic device using the etchant, where the etchant controls the etch rate of a Cu deposition layer (containing Cu, Cu/Ti, or Cu/Ta) over passage of time.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the etchant according to the present invention contains a predetermined additive to control the etch rate of a Cu deposition layer (containing Cu, Cu/Ti, or Cu/Ta) over passage of time. Some examples of the additive may include a chelate having the xe2x80x94COOH group, a chemical compound containing a Cu ion, and a deoxidizer containing sulfur (S).
In one embodiment, the method for fabricating a substrate for an electronic device includes forming a metal thin film containing copper (Cu) on a substrate, selectively exposing the metal thin film, and etching at least one of the exposed and the unexposed portions on the metal thin film with the additive-containing etchant to control the Cu etch rate over time against the number of sheets of processed substrates. The use of the additive-containing etchant according to the present invention results in the formation of the desired etch pattern.
The additive-containing etchant of the present invention improves the profile of the etched Cu, thereby improving functional accuracy and yield of an electronic device. Furthermore, since the change in an etchant over passage of time is controlled, the replacement period for the etchant is prolonged, thereby lowering production costs because of less frequent etchant replacements.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.